Various means have been used in the prior art to insure the initiation of a grenade upon impact and its self-destruction after a period of time after impact to prevent the grenade from being picked up by unfriendly troops and thrown back. One of the problems with prior art devices has been that in order to accomplish these two functions in their proper sequence required the use of mechanisms which had many complicated parts. Such prior art devices because of their numerous parts and complexity are costly to make and are particularly unsuitable for use in low cost reusable practice grenades. Another problem with prior art fuzes utilizing delay columns has been the premature detonation of the device because of malassembly, missing parts, or abuse. The present invention overcomes these aforementioned problems by its unique design.